In IP communications, various communication parameters are used. For example, there are IP addresses of a communication destination and a communication source, port numbers of the communication destination and the communication source, a Path MTU (Maximum Transmission Unit), a window size, a RTT (Round Trip Time), a retransmission timer, and the like. Furthermore, these communication parameters may include, for example, information as to whether or not communication is possible with the communication destination node, and the cause of an interrupted communication. Hereinafter, the term “communication parameter” as used herein means any information that may be used when IP communications are performed and is independent of network layers.
In IP communications, there exists a function (algorithm) that can learn such communication parameters and find them. With this function or algorithm, the communication parameters are optimally set to achieve, for example, scalability and distributed collaboration. For example, the Path MTU Discovery detects the minimum MTU of links on a path. Furthermore, a slow-start algorithm increases the number of transmitted segments, in other words, adjusts a window size every time ACK is received in order to avoid congestion. According to an Internet Control Message Protocol (ICMP), in the case where a communication with a communication destination node cannot be performed in a normal manner, a communication source node can recognize this fact (type=3) and the cause thereof (code=0 (Network Unreachable), 1 (Host Unreachable), and so on).
However, such a learning and finding function itself also increases workloads, and hence, the following method is proposed. Patent Document 1 described below proposes a method of: installing, in a Provider Backbone Bridge Network (PBBN), a provider backbone network (PBN) database storing information on MAC addresses of all devices that belong to each PBN; and achieving label switching transfer in the PBBN using information in this PBN database, thereby preventing the increase in the workload for learning addresses even if the number of the PBN increases. Patent Document 2 described below proposes a method of registering, in a retransmission timeout table, the maximum RTT value measured in each connection for each host computer serving as a communication target, and using the maximum RTT value as a retransmission timer for new connection, thereby eliminating calculation of the retransmission timeout for each connection, which is unnecessary wastage.